1. Field of the Invention
The present invention relates to a bearing apparatus, a spindle motor, and a disk drive apparatus.
2. Description of the Related Art
Spindle motors arranged to rotate disks about central axes thereof are typically installed in hard disk apparatuses and optical disk apparatuses. Such spindle motors include a stationary portion fixed to a housing of the apparatus and a rotating portion arranged to rotate while supporting the disk(s). The spindle motor is arranged to produce a torque centered on the central axis by magnetic flux generated between the stationary and rotating portions, whereby the rotating portion is caused to rotate with respect to the stationary portion.
The stationary and rotating portions of the spindle motor are joined to each other through a bearing apparatus. In recent years, in particular, spindle motors have often been provided with a bearing apparatus in which a lubricating fluid is arranged between the stationary and rotating portions. The structure of a known bearing apparatus using the lubricating fluid is described, for example, in JP-A 2009-136143.
In some bearing apparatuses using the lubricating fluid, a pumping seal including a plurality of grooves is arranged in the vicinity of a surface of the lubricating fluid. Once the spindle motor is started, the pumping seal causes the lubricating fluid to be drawn inward toward an interior of the bearing apparatus. This contributes to preventing the lubricating fluid from leaking out of the bearing apparatus. In known bearing apparatuses, such a pumping seal is often defined in a radial gap where a surface of a stationary portion and a surface of a rotating portion are radially opposed to each other.
In recent years, there has been a strong demand for a reduction in axial thickness of spindle motors as a demand for notebook personal computers, tablet personal computers, and the like has been increasing. However, when the pumping seal is defined in the radial gap as described above, it is necessary to secure a relatively large axial dimension of the pumping seal to allow the plurality of grooves to be defined in the pumping seal. This need is a factor that hinders a reduction in the thickness of the spindle motors.
In this connection, in the bearing apparatus described in JP-A 2009-136143, the pumping seal is defined in a thrust gap where a surface of a bearing component and a surface of a rotor component are axially opposed to each other (see paragraph and FIG. 1 of JP-A 2009-136143). This arrangement makes it possible to reduce the axial dimension of the pumping seal as compared to the case where the pumping seal is defined in the radial gap.
In the bearing apparatus described in JP-A 2009-136143, however, the lubricating fluid has upper and lower surfaces at two different locations, and the level of the lower surface of the lubricating fluid rises when the pumping seal causes the upper surface of the lubricating fluid to be drawn inward toward an interior of the bearing apparatus. Therefore, it is necessary to secure a relatively large axial dimension of a seal gap arranged to hold the lower surface of the lubricating fluid. This need is another factor that hinders a reduction in the thickness of the spindle motors.